Patent GB-775503-A (GB)
Title: Servo motor systems
IPC: G05D1/08
Filed: 1954-12-08
Abstract: 775,503. Automatic steering control systems. SPERRY CORPORATION. Dec. 8, 1954 [Dec. 8, 1953; Jan. 13, 1954], No. 35578/54. Class 38 (4). In an aircraft automatic pilot a servomotor operating a control surface is energized from an amplifier to which are applied signals dependent on displacement of the aircraft about an axis, rate of such displacement, and movement of the control surface, at least one of these signals being varied by a motor in dependence on a comparison between a signal dependent on displacement of the aircraft about the axis and a signal dependent on movement of the control surface. In Fig. 1 a primary A.C. control signal, derived from the pitch pick-off 14 of a gyrovertical 26, controls, through a servo-amplifier 16, a two-phase servomotor 11 operating elevators 25 to maintain a desired pitch attitude. A rate component of the control signal derived by a network 20, and an A.C. follow-up signal from a variable inductive device 24 operated by servomotor 11 are applied to the input of servoamplifier 16. The primary control signal is also de-modulated at 35 and applied to a simulating network 38 which has a response equivalent to the servo-system under normal load conditions so that through a rate network 40 and a rectifier 41 a direct voltage is produced across a resistor 42 representative of the rate of movement of the elevators under normal load conditions. This direct voltage is compared with a second direct voltage produced across a resistor 34 representative of the actual rate of movement of the elevators. This second direct voltage is derived from the follow-up signal through a modulator 30, a rate network 32 and a rectifier 33. Any difference between the two direct voltages is applied to a modulator 27, the output of which operates a motor 48 to adjust a variable inductive device 45 and thereby vary the supply to variable inductive device 24. This additional control is in such sense as to reduce to zero the difference between the two direct voltages and thus produce the same elevator response to a given primary control signal under all load conditions. A similar arrangement applied to a system for controlling the rudder from a directional gyro is described with reference to Fig. 4 (not shown). In this arrangement separate inductive devices coupled to the servomotor apply signals to demodulator 30 and amplifier 16 and simulating and rate networks 38, 32 and 40 are dispensed with so that a sustained primary control signal may maintain the rudder in a specific position. In modified arrangements for controlling pitch, Figs. 6 and 7 (not shown), the two direct voltages compared are dependent on the rate of change of input to the servo-amplifier and the rate of movement of the elevators, respectively, the circuit for deriving the latter voltage including a simulating network having a response equivalent to that of the aircraft about its pitch axis under normal load conditions. In this case the difference voltage controls the proportion of the primary control signal and follow-up signal combined or the rate component of the primary control signal applied to the input of the servo-amplifier.